Screw and lock washer assembly



April 5, 1938. Q W H 2,113,425"

SCREW AND LOC K WASHER ASSEMBLY Filed Oct. 23, 1937 3 Sheets-Sheet lApril 5, 1938. Q CROWTQHER 2,113,425 7 SCREW AND LOCK WASHER ASSEMBLYFiled 001;. 23, 1937 5 Sheets-Sheet 2 i I I I v, A 54 A fizf zivrEEmmzdCCrowt/zer 3 5Qoyzi7fio0ia my;

April 1933. E. c. CRQWTHER 7 2,113,425

SCREW AND LOCK WASHER ASSEMBLY Filed Oct. 25, 1937 3 Sheets-Sheet 3-fuanlorr 153mm; 0 cma/z/zer @k'wfm W Patented Apr. 5, 1938 UNITEDSTATES SCREW AND LOCK WASHER ASSEMBLY Edmond c. .Crowther, Philadelphia,Pa.) assignor to Illinois Tool Works, Chicago, 111., a corporation ofIllinois Application October 23, 1937, Serial No. l70,634

11 Claims. ,(Cl.15132) This invention relates generally to screw andlock washer assemblies and to methods of producing such assemblies.

The usual method of assembling screws and look washers and subsequentlyapplying the 'assembly to a work piece, for example, to the structure ofan automobile in the process of its construction, consists in manuallyselecting a screw, manually Selecting a lock washer, manuallyassociating the screw and lock washer by relatively moving the threadedshank of the screw and the lock washer axially, and finally applying'these associated parts to the work. Under such circumstances the lockwasher is not associated 'or combined with the screw'in a manner tosecure the washer against axial displacement after it is juxtapositionedwith respect to the clamping Surface of the screw head. Hence, it hasbecome common practice toposition screws with the threaded shankextending upwardly, and then drop lock washers over the screw shanks. Inthis vertical position theseassembled parts must not be disturbed untilthey are-ready for' convolution next adjacent the washer to serve as anabutment-in preventing axial displacement of the lock washer. Assembliesof this kind may be very economically produced, thereby eliminating to aconsiderable degree the time and expense involved in the manualassociation of screws and lock washers which is now practiced in thecommercial field.

Not only is the present invention concerned with the aforesaid simpleand effective method of producing screw and lock washer assemblies, butalso with the production of a new and improved screw and lock washerassembly per se. Lock washers which, to my knowledge, have experiencedgreatest commercial success, have been those of the type having workengaging teeth in the form of corners or edges projecting above andbelow the body portion of the lock washer. Various types of lock washersof this class have been in use and efforts have been made in the of thescrew head, thereby enabling the thread production of such devices torender them applicable to all sizes of screws. Certain types of screws,for example, fillister head screws and others are equipped withrelatively narrow clamping surfaces. This means that, when conventionalmethods of assembling screws and lock washers are employed, the totalradial width of the washer must not exceed the total radial width of theclamping surface of the screw head. Be-

cause the work is countersunk to receive a fillister head screw, thelock washer used with such a screw must not "extend outward beyond theperiphery of the screw head. Difficulty has been experienced insupplying lock washers which will-function with equal effectiveness onscrews having heads provided with either narrow or relatively wideclamping v surfaces. In other words, the standardization of lock washersof.

the toothed or. pronged type for various sizes of clamping Surfaces onscrew heads has not been satisfactorily accomplished. The presentinven-) tion overcomes the above mentioned and other disadvantages andinconveniences by presenting a screw and lock washer assembly whereinthe standardization of lock washers to accommodate various widths ofclamping surfaces on screw heads is accomplished.

More specifically, it is an object of the present invention to provide ascrew and lock washer assembly, as set forth above, wherein lock washershaving apertures of less diameter than conventional lock washers may beemployed to thereby aiford increased axial width in the lock washerstock and thus enable the use of locking edges .which will lockinglyengage with the required toothed type may have all of the internalextremities oi the teeth positioned between the underside of the screwhead and the thread convolution providing an abutment without affectingor impairing the locking effectiveness of the internal teeth.

The invention contemplates screw and lock washer assemblies, asset forthabove, provided withlock washers having either external or internalteeth which present a plurality of work engaging edges for effectivelyand lockingly en gaging the complementary surfaces of the screw head andwork,

The foregoing and numerous other objects and advantages will be moreapparent from the following detailed description when considered inconnection with the accompanying drawings,

wherein- Figure 1 is a side elevational view of a screw blank which isrepresentative of one of the many types of screw blanks which may beused in following the teachings of the present invention;

Figure 2 discloses the screw blank of Figure 1 with an internal toothlock washer associatedv therewith;

Figure 3 discloses the blank of Figure 2 after the thread has beenrolled thereon so as to increase the diameter sufficiently to preventaxial displacement of the lock washer;

Figure 4 is an enlarged elevational view of the upper portion of thedevice shown .in Figure 3, a part of the screw and lock washer beingbroken away to more clearly illustrate the manner in which the lockwasher teeth are operatively retained in position beneath the screwhead; dotted lines indicate the operative position of a lock washer ofconventional design having an internal diameter sufliciently-large topermit it to pass over the screw threads;

Figure 5 is a fragmentary transverse sectional view taken substantiallyalong the line 55 of Figure 3;

Figure 6 is an enlarged detail view of one of the internal lock washerteeth and associated body portion, the body portion being shown insection;

Figure 7 is an end elevational view of the lock washer tooth or prongshown in Figure 6, said view being taken from the right of Figure 6;

Figure 8 is a fragmentary vertical sectional view similar to Figure 4,disclosing a lock washer having modified locking teeth secured beneaththe screw head;

Figure 9 is a fragmentary transverse sectional view taken substantiallyalong the line 99 of Figure 8.;

Figure 10 is an end elevational view of the washer teeth shown inFigures 8 and 9, said view being taken substantially along the lineiii-l0 of Figure 9;

Figure 11 discloses an external tooth washer positioned beneath the headof a screw blank before rolling the thread thereon;

Figure 12 discloses the blank of Figure 11 after the thread has beenrolled thereon;

Figure 13 is a fragmentary enlarged elevational view of the upperportion of the assembly shown in Figure 12, a part of the screw and lockwasher being broken away to more clearly illustrate the manner in whichthe locking teeth are operatively secured in position beneath the screwhead;

Fi ure 14 is an enlarged fragmentary sectional view ofthe screw and lockwasher assembly taken substantially along the line i4--l4 of Figure 13;

Figure 15 illustrates the manner in which lock washers of conventionalsize when slipped over the thread of a screw, extend radially outward aconsiderably greater distance than the lock washers assembled withscrewheads in the manner disclosed and,claimed herein;

Figure 16 is a fragmentary sectional view similar to Figure 13,disclosingan external tooth lock washer of modified form associated,with the clamping surface of a screw head as contemplated by thepresent invention;

Figure 17 is a fragmentary sectional view taken substantially along theline |'i-|'| of Fig- I fillister heads, Figure 19 disclosing a screw andlock washer assembly contemplated by the present invention, in which aninternal tooth lock washer is in operative association with a screwhaving a hexagon head;

Figure 20 is a transverse sectional view taken substantially along theline 20-40 of Figure 19;

Figure 21 is a fragmentary view, similar to Figure 20, showing theposition occupied by a conventional internal tooth lock washer to ahexagon head;

Figure 22 is a side elevational view, similar to Figure 19, disclosingthe application of an external tooth lock washer to a screw having ahexagon head;

Figure 23 is a transverse sectional view'taken substantially along theline 2323 of Figure 22; and I Figure 24 illustrates the positionoccupied by a conventional external tooth lock washer when applied tothe hexagon head of a screw.

Referring now to the drawings more in detail wherein like numerals havebeen employed to designate similar parts throughout the various figures,it will be noted that the invention contemplates the production of ascrew and lock washer assembly which is designated generally by thenumeral 20 in Figures 3 and 4. This screw and lock washer assembly 20includes a screw element 22 comprising a threaded shank 24 and a head 26presenting a clamping surface 28 extending outwardly beyond theperiphery of the threaded shank. A lock washer designated generally bythe numeral 30 is operatively secured against axial displacement beneaththe clamping surface 28 by the uppermost thread convolution of thethreaded shank 24. The internal diameter of the lock washer 30 issufliciently less than the external diameter of said uppermost threadconvolution to enable the washer to be secured against axialdisplacement.

The screw and lock washer assembly 20 is produced by employing a screwblank 32 shown in Figure 1, the shank portion of which has a diameterwhich is slightly less than the internal di-' ameter of the lock washerso as to permit said parts to be brought into association with eachother, as illustrated in Figure 2. After the screw and lock washer havebeen thus associated, the shank of the screw blank 32 is rolled betweenthreading dies so as to produce the threaded shank 24 shown in Figure 3.During this rolling process the external diameter-of the shank isincreased sufficiently in the vicinity of the screw head 26 to providean abutment which precludes axial displacement of the lock washer.

Particular attention is directed to the structural characteristics ofthe lock washer 30 and the manner in which the lock washer structurecooperates with the screw element in presenting a new and improved screwand lock washer assembly. The lock washer 30 is of the type commonlyreferred to as an internal tooth lock washer, and includes an annularbody portion 34 of spring stock and a plurality of internalcircumferentially spaced locking elements or prongs 36. These prongs areso configurated, warped, or twisted as to present work engaging edges 38positioned on opposite sides of the body 34. It will be noted that theseedges 38 in the present embodiment lie in planes spaced from andsubstantially parallel with the bounding planes of the body portion 34,and are so disposed as to make a line bite in the clamping surface 28 ofthe screw and the complementary surface of the work when the screw istightened against the washer. While the inner extremities of the prongs36 extend inwardly with respect to the outer periphery of the threadedshank 24 a sufficient distance so as to cooperate with the uppermostthread convolution in securing the lock washer and screw against axialdisplacement, the locking edges 38 extend radially outward beyond theperiphery of the threaded shank. Thus, the portion of each locking edge38, as indicated by the bracket A in Figure 6, which extends radiallyoutward beyond the periphery of the threaded shank 24, is in a positionto embed itself within the complementary surface of the work piece orscrew head when the parts are clamped together. That is to say, a smallportion of each prong is positioned between the uppermost screwconvolution and the inner portion or zone of the screw head, but themajor portion of each prong and consequently the locking teeth thereofis positioned radially outward beyond the peripheral limits of thethreaded shank in a position to effectively and aggressively perform theintended locking action.

Particular attention is directed to the practical advantages which flowfromthe use of the above describedscrew and lock washer assembly. Forthe purpose of illustrating one of the many practicai advantages, ascrew equipped with a relatively narrow clamping surface on the headthereof is shown. This type of screw is sometimes referred to as afillister head screw. A screw of this type is usually inserted within acountersunk aperture in the work. as clearly illustrated in Figure 4.-In view of this use, a lock washer cannot be employed which extends toany appreciable degree beyond the peripheral limits of the screw head26. Furthermore, fillister head screws and other screws in common usehave relatively narrow clamping surfaces as aforesaid, and hence make itextremely difficult to provide a suitable lock washertherefor. It iscommon practice, as previously stated, to use lock washers having aninternal diameter which is slightly greater than the external diameterof the threaded shank. Thus, when screws of the type disclosed hereinare equipped with a conventional lock washer. a condition exists whichis illustrated by the dotted lines in Figure 4. These dotted linesdisclose the position of the teeth and annular body of a conventionallock washer when applied to the screw in a conventional manner. the dotand dash lines indicating the screw blank before rolling. Under suchcircumstances the annular body extends an appreciable distance beyondthe periphery of the screw head, and this precludes the use of such lockwashers on that type of head.

The present invention solves the problem of providing screw and lockwasher assemblies in which the lock washer element thereof has beenreduced in internal diameter sufficiently to, in effect, move the entirelock washer structure inwardly by an amount which brings the outwardperiphery of the washer in line with the outer 34 of suflicient radialcross-section to provide the r required resilient support for theteethor prongs, and the teeth 36 occupy anv effective work engaging orlocking position It will also be observed that, when the lock washer. 30has been associated beneath the screw head, as previously de-- scribed,and the inner extremities of the prongs or looking elements-36 becomepositioned between an innermost clamping zone of the screw head and theuppermost thread convolution, the

possibility of the lock washer subsequently becoming unscrewed from thethreaded shank is reduced to a minimum.' That is to say, the maximumover-all axial width of the lock washer, measured from the plane,including the locking edges 38 on. one side to the plane including thelocking edges 38 on the other side, is suflicient to preclude thepossibility of the lock washer prongs falling into the helical pathprovided by the screw threads. This is an important feature consideredfrom the standpoint of maintaining the proper assembled relationship ofthe screw and lock washer from the time the assemblies have beenmanufactured until they reach the ultimate user thereof. Such parts intransit are subjected to considerable vibration and jarring and, as aresult, there is the potential possibility of disassembly of the partsconstituting each assembly, if it were possible for the lock washerteeth to pass through or within the helical path provided by the screwthreads. The sufficiency in maximum axial over-all width of the washer.teeth, as just mentioned, positively prevents the loosening or partialseparation of the constituent parts by unscrewing.

Obviously the lock washer 30 is in no sense limited for use withrelatively narrow clamping surfaces of screw heads, but is capable ofapplication to either narrow or relatively wide clamp- Thus one size oflock washer ing surfaces. may be used to accommodate a relatively widerange of screw head clamping surfaces. In this way the standardized useof lock Washers for and lock washer assembly may be produced. The

internal teeth or prongs of the lock washer 30 are so'disposed with'respect to the screw thread and clamping surface as to insure lockingengagement of the portions'A of the washer teeth '36 with the clampingside of the screw head and the work surface, even though the innerextremities of each washer prong or'tooth extendsinwardly of thethreaded shank. This feature of construction, coupled with an effectiveline-biting or embedding of oppositely disposed teeth within thecomplementary surfaces between which they are clamped, provides a screwand lock washer assembly in which locking efficiency is maintained atits maximum.

Obviously the invention is not limited to any specific formof screw orlook washer, but contemplates structures of varied forms. Forillustrative purposes a modified lock washer, designated generally bythe numeral 30a (Figures. 8 to 10, inclusive) is disclosed. This lockwasher is also of the internal tooth or prong type, and includes anannular body portion 34a and internal prongs or elements 36a havingoppositely disposed work engaging and biting edges 38a. Each of theteeth 36a has a portion A, as indicatedin Figure 8, which extendsradially outward from the periphery of the threaded shank correspondingwith the portion A of the teeth 36 (Figure 6). A small portion of theinner extremities of the prongs or elements 36 is positioned between aninnermost zone of the clamping surface 28 and the uppermost threadconvolution, as previously described in connection with Figures 1 to '7,inclusive. Thus, a screw and lock washer assembly is provided, in whichlocking teeth of slightly different form from the teeth previouslydescribed function effectively to secure the screw against retrogrademovement, and the internal diameter of the lock washer is suflicientlyreduced to enable the use of such washers with screw heads of the typeshown herein. Likewise, lock washers of the type designated by thenumeral 30a herein may be standardized for use with clamping surfaces ofvaried widths, thereby greatly facilitating the production of screw andlock washer assemblies. The screw and lock washer assembly equipped withthe lock washer 36a. is designated generally by the numeral 20a inFigure 8.

Thus far the invention has been described in connection with the use ofscrew and lock washer designated generally by the numeral 30b includesan internal, annular body portion 34b from which radiate a plurality ofcircumferentially spaced locking elements or prongs 36b. Each of thelocking elements or prongs 361) have oppositely disposed work engagingand locking edges 36b which are positioned in parallel planes spacedfrom and positioned on opposite sides of the bounding planes of the body34b. The locking elements or prongs 36b are similar in structuralcharacteristics to the locking prongs 36 previ-- ously described, theonly difference being that the prongs 36b extend outwardly from theannular washer body.

The lock washer-30b is assembled with the screw in the same manner asdescribed in connection with the screw assemblies 20 and 20a. The washer36b is first applied to the screw blank 32, as illustrated in Figure 11,the internal diameter of the lock washer being just sumcient to receivethe shank of the blank 32. The thread on the shank is subsequentlyrolled, thereby increasing the diameter sufficiently so as to enable theuppermost thread convolution to secure the lock washer against axialdisplacement. In Figure 13 the unthreadcd blank, as it appears beforerolling the thread thereon, is indicated by dot and dash lines.

As previously described in connection with the screw and lock washerassemblies 20 and 20a, the internal diameter of the lock washer 30b isless than the internal diameter of conventional lock washers which haveheretofore been'em-' ployed and hence the entire lock washer stock,including in radial widththe internal, annular body 34b and the prongs36b, is in effect shifted bination withscrew heads of relatively narrowwidth. As shown in Figure 15, if the screw head 26 is associated withthe lock washer X, a portion of the locking edges of the prongs willextend outwardly beyond the clamping zone of the screw head. In otherwords, the locking effectiveness of the lock washer X, when used withthe screw head 26, is materially reduced. Furthermore, when it isappreciated that fillister head screws are usually inserted withincountersunk apertures in the work which have a diame; ter substantiallyequal to the diameter of the screw head, it will be apparent that thelock washer X cannot be used because of the extension of the prongsthereof to a considerable degree beyond the periphery of the fillisterhead, as shown in Figure 15.

Thus, the present invention enables the use in screw and lock washerassemblies of externally toothed or pronged lock washers havingapertures of reduced size, and this feature of construction materiallyenhances the use and manufacture of these look washers in combi tionwith screw heads. Obviously the lock was er 30b will functioneifectively with screw heads having a larger diameter than the screwhead 26. In

other words, a given size of lock washer may be used with completesatisfaction for screw heads having clamping surfaces of varied widths.

The fact is that the present ihvention enables the use of lock washerswhichv will serve to. effectively lock screw heads having a relativelynarrow clamping surface (a result heretofore not obtained with completesatisfaction) and will also serve to lock screws having relatively wideclamping surfaces. The fact that applicant employs the innermost zone ofthe screw, to-wit, the annular area immediately adjacent the heck of thescrew extending between the screw head 26' and the uppermost threadconvolution, to receive the non-locking-portion of the washer, that is,the annular body 34b, permits locking teeth of required radial length tobe used without sacrificing the supporting strength provided by the lockwasher body. In other words, the zone associated with the underside ofthe screw head,-

which otherwise serves no real purpose, is employed inthe presentinvention to receive or accommodate a portion at least of the annularwasher body 341). In so doing, the internal diameter of the washer isreducedwithout affecting the strength or lockingefllciency of the lockwasher. When tne screw head 26 is tightened within the work,theoppositely disposed biting edges 38b efiectively embed themselves inthe complementary surfaces of the screw headand work so as to make aneffective line bite and thereby exertmaximum resistance to unscrewing.

In Figures 16 to 18, inclusive, I have disclosed.

the use of a slightly. modified external tooth washer designatedgenerally by the numeral 300. This lock washer includes an inner annularbody 340 and .a plurality of circumferentially sembly equipped with thewasher 300 is designated generally by the numeral 200. Obviously theinvention is not limited to the use of a specific form of washer teeth,but contemplates various modifications whereby the improved results,accomplished by the disclosed embodiments, are obtained.

In Figures 19 to 24, inclusive, I have illustrated the manner in whichthe present invention facilitates the use of internal andexternal toothlock washers with hexagon heads of screws. The clamping surface ofhexagon heads, like the clampingsurface 28 of the fillister head 26previously described, is often quite narrow in radial width. As aresult,when conventional internal .tooth lock washers are employed, aconsiderable portion of the annular body projects beyond the externalperiphery of the screw head, and, when external tooth lcckwashers areemployed, a considerable portion of each: locking tooth projects beyondthe periphery 'of the hexagon head and thereby materially reduces thelocking effectiveness of said teeth. By employing lock washers ofreduced internal diameter as previously de scribed, these diificultiesare completely overcome.

In Figures 19 and 20 I have shown a screw and lock washer assemblydesignated generally by the numeral 2011, said assembly including ascrew having a threaded shank 24d and a hex head 26d. The assembly 20dis equipped with the internal tooth lock washer 30. Particular attentionis directed to the fact that'the outer periphery of the annular. washerbody is well within the maximum diameter of the hexagon head. In otherwords, .thewasher body does not appear unsightly, nor does it presentany inconvenience to the user of the assembly.

In Figure 21 I have illustrated the manner in which a conventionalinternal tooth lock washer. designated generally by the letter Y, whenapplied .to the hexagon head 26d in the conventional manner by slippingit over the threaded screw shank, has its outer annular body radiallyprojecting a considerable distance be yond the outer periphery of thehexagon head. This condition is' frequently most undesirable.

' In both Figures 20 and 21 the external diameter The screw and lockwasher asbypassing it over the external diameter of said shank. Thiscauses a large portion of the washer teeth to be positioned in ancnlocking or nonfunctional zone with respect to the clamping surface ofthe hexagon head. Thus the locking efiiciency of this lock washer isseriously impaired.

' Comparing thisarrangement with that disclosed in Figures122 and 23, itwill be apparent that the present invention materially contributes tothe efiicicnt functioning of external tooth lock washcrs when applied tohexagon heads having the usual relatively .narrow .clamping surface.

From the foregoing it will be apparent that the present inventioncontemplates a screw and lockwasher assembly of improved practical de-.

sign which serves to materially enhance the ease scribed herein andcontemplated hereby with their reduced innerdiameters, whether they belock washers of the internally or externally toothed variety, when usedin combination with screw heads, make for standardization of production,which in turn reduces the ultimate cost and provides astandardized'product which has heretofore not been available to thetrade.

In practicing the present invention it is preferred to use screw blanksin which the shank portions are substantially cylindrical throughouttheir length and particularly in the vicinity of the head so as toenable the use of lock washers having minimum internal diameters. Inusing internally toothed lock washers, it may be advisable in someinstances to employ teeth or prongs having a radial length slightlygreater'than the radial length of similar lock washers which haveheretofore been employed. In this manner no loss in lockingefiectiveness of the teeth will be as described herein, may be practicedwith the greatest economy,'and this method of assembly makes possiblethe production of a uniform and standardized product.

Another advantage resulting from the present invention is the propercentering of the lock washer with respect to its associated screw. Inusing lock washers such as the lock washers X and Y in the conventionalmanner, thatis, by

passing them over the threaded shank and then applyingthe associatedscrew and lock washer to the work, there is ever present the potentialpossibility of eccentrically positioning the lock washer when the screwisdriven home. This is due to the fact that the inner periphery of thelock washer may enter the valley between the upper thread convolutions,thereby causing the lock washer to be positioned ofbcenter. Under suchcircumstances the eificiency of the lock washer is materially reducedand the external appearance, after the screw has'been driven home, ismost unsightly. Thepresent-invention positively insures the absolutecentering of lock washers, either of the external or internal toothtype, and thus insures the proper positioning of the locking edgesbetween the clamping surface 'of the screw head and the complementarysurface of the work.

While certain specific structural details ofscrews and lock washers havebeen described herein, it will be apparent that the invention is notlimited to these specific embodiments, but contemplates othermodifications and. changes without departing from the spirit and scopeof the appended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A screw and lock. washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer operativelyassociated therewith including a body portion and a plurality of workengaging teeth projecting from opposite sides-of said body portion, saidteeth presenting edges adapted to make a line bite into said clampingsurface and the complementary surface of a work piece when the screw istightened thereinfthe inner diameter of said lock washer beingsufficiently less than the external diameter of the threaded shank torender the thread in the immediate vicinity of the lock washer operableto prevent axial displacement thereof.

'2. A screw and lock washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer operativelyassociated therewith including a body portion and a plurality of workengaging teeth projecting from opposite sides of said body portion, saidteeth presenting edges positioned in planes spaced from andsubstantially parallel with the bounding planes of the body portion, theinner diameter of said lock washer being sufliciently less than theexternal diameter of the threaded-shank to render the thread in theimmediate vicinity of the lock washer operable to prevent axialdisplacement thereof.

3. A screw and lock washer assembly-including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer operativelyassociated therewith including a body portion and a plurality ofexternal work engaging teeth projecting from opposite sidesof .said bodyportion, said teeth presenting edges adapted to make a line bite intosaid clamping surface and the complementary surfaceof a work piece whenthe screw is tightened therein, the inner diameter of said lock washerbeing sufficiently less than the external diameter of the threaded shankto render the thread in the immediate vicinity of the lockwashemoperable to prevent axial displacement thereof.

4. A screw and lock washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank,

' and a lock washer operatively associated therewith including a bodyportion and a plurality of internal working engaging teeth projectingfrom opposite sides of said body portion, said teeth presenting edgesadapted ito make a line bite into said clamping surface jnd thecomplementary surface of a workpiece when the screw is tightenedtherein, the inner diameter of said lock washer being sumcientlyless'than the external diameter of the threaded shank to render thethread in the immediate vicinity of the lock washer operable to preventaxial displacement thereof.

5. A screw and lock washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer operativelyassociated therewith including a body portion and a plurality ofexternal work engaging teeth projecting from opposite sides of said bodyportion, said teeth presenting edges positioned in planes spaced fromand substantially parallel with the bounding planes of the bodyportions, the inner diameter of said lock washer being suiiiciently lessthan the external diameter of the threaded shank to render the thread inth' immediate vicinity of the lock washer operable to prevent axialdisplacement thereof.:

6. A screw and lock washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer operativelyassociated therewith including a body portion and a plurality ofinternal work engaging teeth projecting from opposite sides of said bodyportion, said teeth presenting edges positioned in planes spaced fromand substantially parallel withthe bounding planes of the body portion,the inner diameter of said lock washer being sufficiently less than theexternal diameter of the threaded shank to render the thread in theimmediate vicinity of the lock washer operable to prevent axialdisplacement thereof.

'7. A screw and lock washer assembly including a screw-member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer associatedtherewith including a body portion and a plurality of internal workengaging teeth projecting from opposite sides of. said body portion, thethread on said shank being rolled and having an external diameter in thevicinity of said clamping surface which is greater than the internaldiameter of the lock washer, the inner extremities of said teeth beingpositioned between said clamping surface and the uppermost convolutionof the threaded shank, portions of said teeth extending radially outwardbeyond the external diameter of said thread con volution in operativeposition for lockingly engaging said clamping surface and acomplementary surface of the work when the screw is tightened within thework.

8. A screw and lock washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank,

thread in the immediate vicinity of the lock washer operable to preventaxial displacement thereof.

9. A screw and lock washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer operatlvelyassociated therewith including a body portion and a plurality ofcircumferentially disposed marginal sections bent in opposite directionsout of the plane of said body portion so as to present work engagingedges positioned in planes spaced from and substantially parallel withthe bounding planes of the body portion, the inner diameter of said lockwasher being sufficiently less than the external diameter of thethreaded shank to render the thread in the immediate vicinity of thelock washer operable to prevent axial displacement thereof.

10. A screw and lock washer assembly including a screw member having ashank with an extruded thread and a head presenting a clamping surfaceextending outwardly from the shank.

and a lock washer operatively associated therewith including a bodyportion and a plurality of circumferentially disposed marginal sectionstwisted so as to present work engaging edges positioned in planes spacedfrom and substantially parallel with the bounding planes of. the

body portion, the thread on said shank being rolled and having anexternal diameter in the vicinity of said clamping surface which issufficiently greater than the internal diameter of the lock washer tosecure said lock washer against axial displacement.

11. A screw and lock washer assembly including a screw member having ashank with an ex truded thread and a head presenting a clamping surfaceextending outwardly from the shank, and a lock washer operativelyassociated therewith including a body portion and a plurality ofmarginal prongs, each prong being tapered and progressively twisted fromthe root to the free end thereof so as to present oppositely disposedwork engaging edges adapted to make a line bite into said clampingsurface and the clamping surface of a work piece when the screw istightened therein, the inner diameter of said lock washer beings'uihciently less. than the external diameter of the threaded shank torender the thread in the immediate vicinity of. the lock washer operableto prevent axial displacement thereof. l

EDMOND C. CROWTHER.

